Following unilateral lumbosacral deafferentation of the cat hindlimb, Substance P reaction product demonstrated by the unlabeled antibody (PAP) technique in the lumbar dorsal horn has been shown at first to decrease and then to return. This pattern of change may be interpreted as indicating sprouting by Substance P containing axons. In the coming year the source(s) of these axons will be investigated and the ultrastructure of the sprouting terminals determined. A second with sparing of the L6 root, will also be investigated for sprouting using the PAP method for demonstrating Substance P, and sprouting in this preparation will be correlated with locomotor recovery.